The invention relates to an implantable infusion pump with an elastic medicament container, a propellant chamber acting on the latter and having a propellant formed from a chlorofluorohydrocarbon, as well as a restricting capillary tube.
Implantable infusion pumps are used for the long-term administration of medicaments, e.g. morphine in a constant dose over a long period. Compared with conventional injections, they offer the advantage that it is no longer necessary to overdose to such an extent that despite the breaking down of the medicament up to the next adminstration time there is no drop below a certain minimum dose and instead there is a uniform and significantly reduced supply of the medicament.
However, hitherto in the case of infusion pumps of the aforementioned type problems have occurred when the temperature was changed. If the person with such an infusion pump implanted has fever with a body temperature of 42.degree. C., as a result of the additional expansion of the propellant the delivery can be up to 46% more (propellant: trichlorofluoromethane), which is naturally highly undesired.
Similar problems can occur when the atmospheric pressure is changed. Here, e.g. when staying at an altitude of 3000 m, which roughly corresponds to atmospheric pressure and which can occur in an aircraft, there can even be an additional delivery of 55%.
The problem of the invention is therefore to provide an implantable infusion pump, in which such effects play a very minor part and the operational reliability of the pump is improved.